BR112015022405B1 - METHOD IMPLEMENTED BY A CABLE MODEM TERMINATION SYSTEM, CMTS - Google Patents

Abstract

CENTRAL ACCESS NETWORK UNIT, NETWORK UNIT IN A COAXIAL NETWORK, AND METHODS IMPLEMENTED BY A CMTS OR CLT The present invention relates to a central access network unit comprising a processor (330) configured to assign a plurality of upstream training blocks from an upstream OFDM symbol to a plurality of downstream network units, the OFDM symbol comprising a plurality of equally spaced pilot subcarriers s over an upstream RF spectrum at a predetermined time interval, and wherein each upstream training block comprises a different subset of the pilot subcarriers that are non-consecutive and located across the upstream RF spectrum, and generate one or more messages comprising assignments from the upstream training blocks, and a transmitter (310) coupled to the processor (330) and configured to transmit the messages to the plurality of downstream network units across a network, wherein the messages instruct at least one of the plurality of downstream network units for transmitting a predetermined modulated sequence on the pilot subcarriers corresponding to the upstream training block (...).

Description

BACKGROUND

[001] A Passive Optical Network (PON) is a system for providing network access in the last mile. PON can be a point-to-multipoint (P2MP) network with passive splitters positioned in an optical distribution network (ODN) to enable a single distribution fiber from a switch to serve multiple customer sites. PON can employ different wavelengths for upstream and downstream transmissions. Ethernet Passive Optical Network (EPON) is a PON standard developed by the Institute of Electrical and Electronics Engineers (IEEE) and specified in IEEE documents 802.3ah and 802.3av, both of which are incorporated herein by reference. Hybrid access networks employing EPON or other network types have attracted increasing attention.

SUMMARY

[002] In one embodiment, the disclosure includes a central access network unit comprising a processor configured to assign a plurality of upstream training blocks from an upstream orthogonal frequency division multiplexing (OFDM) symbol to a plurality of downstream network units, the OFDM symbol comprising a plurality of equally spaced pilot subcarriers across an upstream radio frequency (RF) spectrum at a predetermined time interval and each upstream training block being comprising a different subset of pilot subcarriers that are non-consecutive and located across the upstream RF spectrum, and generating one or more messages comprising assignments of the upstream training blocks and a transmitter coupled to the processor and configured to transmit the messages to the plurality of downstream network units over a network, the messages instructing at least one of the plurality of downstream network units to transmit a predetermined sequence modulated on the pilot subcarriers that corresponds to the upstream training block assigned to the unit downstream network.

[003] In another embodiment, the disclosure includes a method implemented by a Cable Modem Termination System (CMTS) comprising allocating a polling symbol within a polling frame, the polling frame comprising a variable k number of contiguous welding symbols, and each polling symbol comprising a plurality of equally spaced subcarriers across a frequency spectrum upstream of a cable TV service data interface specification (DOCSIS) network at a time interval predetermined, defining a polling pattern on the allocated polling symbol, wherein the polling pattern comprises a set of sparse subcarrier pilots of the allocated polling symbol, and instructing a Cable Modem (CM) to transmit a polling sequence on the allocated polling symbol according to the defined polling pattern.

[004] In another embodiment, the disclosure includes a method deployed by a Coaxial Line Terminal (CLT) comprising allocating a specific polling symbol to a Coaxial Network Unit (CNU) within a polling frame for upstream broadband polling, the polling symbol comprising a plurality of equally spaced pilots across an upstream spectrum of a passive optical Ethernet network over coax (EPoC) at a predetermined time interval, allocating a subset of pilots sparse within polling symbol to CNU, receive polling symbol from CNU, perform upstream channel estimation from polling symbol received.

[005] In yet another embodiment, the disclosure includes a network unit in a coaxial network comprising a receiver configured to receive a message indicating an upstream training block assigned in an upstream OFDM symbol comprising a plurality of equally spaced pilot subcarriers in a frequency spectrum of the network unit at a predetermined time interval and wherein the upstream training block comprises a subset of pilot subcarriers that are non-consecutive and located across the frequency spectrum, a processor coupled to the receiver and configured to generate the upstream training block by modulating a predetermined sequence on the pilot subcarriers of the upstream training block and a transmitter coupled to the processor and configured to send the upstream training block over the coaxial network.

[006] This and other features will be more clearly understood from the following detailed description taken in conjunction with the attached drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[007] For a more complete understanding of this disclosure, reference is made to the following brief description, taken in connection with the accompanying drawings and detailed description, similar reference numbers representing similar parts.

[008] Figure 1 is a schematic diagram of a network modality

[009] Figure 2 Optical coaxial is a unified diagram. schematic of a network modality

[010] Figure 3 DOCSIS is a . Schematic diagram of one embodiment of a network element (NE), which can act as a node in an EPoC network and/or a DOCSIS network.

[011] Figure 4 is a schematic diagram of one embodiment of a probe symbol comprising an upstream training block.

[012] Figure 5 is a schematic diagram of another embodiment of a probe symbol comprising an upstream training block.

[013] Figure 6 is a schematic diagram of another embodiment of a probe symbol comprising three upstream training blocks.

[014] Figure 7 is a flowchart of one embodiment of an upstream training method.

[015] Figure 8 is a flowchart of another embodiment of an upstream training method.

[016] Figure 9 is a schematic diagram of an embodiment of an upstream training message encoding.

[017] Figure 10 illustrates a graph of one embodiment of upstream signal-to-noise ratio (SNR) loss as a function of the number of downstream sounding network units in a single sounding symbol.

DETAILED DESCRIPTION

[018] It should be understood at the outset that, although an illustrative implementation of one or more embodiments is provided below, the systems and/or methods disclosed may be implemented using any number of techniques, known or existing. Disclosure shall in no way be limited to the deployments, drawings and techniques illustrated below, including the exemplary designs and deployments illustrated and described herein, but may be modified within the scope of the appended claims together with the full scope of equivalents thereof.

[019] Some hybrid access networks can combine optical networks with coaxial networks (coax). Ethernet over Coax (EoC) may be a generic name used to describe all technologies that transmit Ethernet frames over a coaxial network. Examples of EoC technologies might include EPoC, DOCSIS, Multimedia over Coax Alliance (MoCA), G.hn (common name for a home networking technology family of standards developed by the International Telecommunications Union (ITU) and promoted by the HomeGrid Forum), Home Telephone Line Network Alliance (HPNA), and Home Audio-Visual (A/V) cable. EoC technologies may have been adapted to perform external coax access from an Optical Network Unit (ONU) to an EoC head end with connected customer premises equipment (CPEs) located in subscriber homes. In a coaxial network, physical layer transmission can employ OFDM to encode digital data on multiple carrier frequencies. Some advantages of OFDM transmission may include high spectral efficiency and robust transmission (eg attenuation at high frequencies in long coaxial wires, narrowband influencers, frequency selective noise, etc.).

[020] An EPoC system can be a hybrid access network that employs coaxial or optical technologies. The EPoC may comprise an optical segment which may comprise a PON and a coaxial segment which may comprise a coaxial cable network. On the PON segment, an OLT can be positioned at a local exchange or central office where the OLT can connect the EPoC access network to an Internet Protocol (IP), Synchronous Optical Network (SONET) and/or Asynchronous Transfer Mode (ATM) Backbone. On the coaxial segment, CNUs may be positioned at end-user locations and each CNU may serve a plurality (eg, three to four) of end-users which may be known as subscribers. A Fiber Coaxial Unit (FCU) can combine the interface between the PON segment and the coaxial segment of the network. The FCU can be a single box unit that can be located where an ONU and CLT are fused together, for example on a parapet or curb or in a portion of a building. The CLT or FCU can employ OFDM transmission in a physical layer to communicate with the CNUs.

[021] A DOCSIS network can operate with a hybrid fiber coaxial network (HFC) and can be structurally similar to an EPoC network. The DOCSIS network can comprise a CMTS positioned at a local exchange or central office where the CMTS can connect the HFC network to a main network. The CMTS can serve a plurality of CMs positioned at end-user locations. In some embodiments, a CMTS may be integrated with OFDM P2MP communication functionalities (eg, channel estimation, scheduling).

[022] In OFDM communication, a physical layer channel can be established before data transmission, for example, by performing training and/or channel estimation. In one embodiment, a CLT may assign an upstream OFDM symbol (eg, polling symbol) for upstream channel measurement (eg, upstream polling). The probe symbol may span time and frequency, for example the probe symbol may comprise a plurality of subcarriers (e.g. pilot subcarriers) equally spaced across an entire upstream RF spectrum (e.g. symbol channel bandwidth) at a predetermined time interval (e.g. one symbol time). A CNU may transmit a predetermined wideband sequence (e.g., pilot sequence or polling sequence) in the polling symbol using all pilot subcarriers in the polling symbol. When the CLT receives the probe symbol, the CLT can estimate upstream channel conditions between the CNU and the CLT on each of the pilot subcarriers by comparing the received signal to the predetermined bandwidth sequence. In order to differentiate upstream transmissions between different CNUs, the CLT may assign a separate polling token to each CNU. However, the channel bandwidth for upstream polling can increase as the number of connected CNUs increases in a network and thus can result in lower bandwidth efficiency. It should be noted that in the present disclosure, the terms upstream training and probing are equivalent and may be used interchangeably. Additionally, the terms FCU and CLT are equivalent and can be used interchangeably.

[023] An upstream pilot scheme that can be performed by an OFDM P2MP communication system (for example, a CLT or a CMTS) in a hybrid access network (for example, an EPoC network or a DOCSIS network) is disclosed in this document. An OFDM P2MP communication system may assign an upstream OFDM symbol as a polling symbol for measuring upstream channels between a plurality of downstream network units and the OFDM P2MP communication system. In one embodiment, a CLT or CMTS can assign a plurality of upstream training blocks from a probe symbol to a plurality of CNUs or CMs, respectively, where each upstream training block can comprise a different subset of pilot subcarriers that are non-consecutive and span across the upstream frequency spectrum. A CNU or a CM can transmit a high-bandwidth pilot sequence on the pilot subcarriers of an assigned upstream training block. The CNU or CM can insert frequency nulls (e.g. values of zero) into unassigned pilot subcarriers (e.g. excluded subcarriers) so that the CNU or CM cannot interfere with other CNUs or CMs that transmit with a different set of pilot subcarriers on the same probe symbol. As such, the plurality of CNUs or CMs may transmit a different portion of the high-bandwidth pilot sequence on a different pilot subcarrier set simultaneously within the polling symbol duration. In one embodiment, the upstream training block may be specified in terms of an initiating pilot subcarrier and a fixed number of subcarriers for jumping between successive assigned pilot subcarriers. The disclosed upstream pilot scheme can utilize upstream bandwidth efficiently by allowing multiple CNUs or CMs to transmit simultaneously on the same polling symbol, and can provide comparable upstream SNR performance as an upstream pilot scheme that allocates one polling symbol per CNU or CM. Additionally, the disclosed upstream pilot scheme may allow a CMTS or CLT to probe a CNU or CM with a lack of power (e.g., long distance and/or high attenuation channel) successfully by employing only a subset of the subcarriers of the OFDM symbol, where the CNU or CM may not have enough power to send a probe sequence with adequate power across all subcarriers of the OFDM symbol.

[024] Figure 1 is a schematic diagram of one embodiment of a unified optical coaxial network 100 comprising an optical portion 150 and a coaxial (electrical) portion 152. The network 100 may include an OLT 110, at least one CNU 130 coupled to a plurality of subscriber devices 140, and a CLT 120 positioned between the OLT 110 and the CNU 130, for example , between the optical portion 150 and the coaxial portion 152. The OLT 110 may be coupled via an ODN 115 to the CLTs 120, and optionally to one or more ONUs 170, or one or more HFC nodes 160 on the optical portion 150. The ODN 115 may comprise optical fibers and an optical splitter 117 and/or a cascade of 1 x M passive optical splitters that couple OLT 110 to CLT 120 and any ONUs 170. The value of M in EPoC, eg the number of CLTs, can be eg 4, 8, 16 or other values and can be selected by the operator depending on factors such as optical power reserve. The CLT 120 may be coupled to the CNUs 130 via an electrical distribution network (EDN) 135, which may comprise a cable splitter 137, a cascade of taps/splitters and/or one or more amplifiers. Each port of OLT 110 can serve 32, 64, 128 or 256 CNUs 130. It should be noted that upstream transmissions from CNUs 130 can reach the CLT 120 and not the other CNUs 130 due to a directional property of the branch. The distances between the OLT 110 and the ONUs 170 and/or the CLTs 120 can vary from about 10 to about 20 kilometers (km) and the distances between the CLT 120 and the CNUs 130 can vary from about 100 to about 500 meters (m). The network 100 may comprise any number of corresponding HFCs 160, CLTs 120 and CNUs 130. Network components 100 may be arranged as shown in Figure 1 or any other suitable arrangement.

[025] The optical portion 150 of the network 100 can be similar to a PON in that the optical portion 150 can be a communications network that does not require active components to distribute data between the OLT 110 and the CLT 120. Instead, the optical portion 150 can use the passive optical components in the ODN 115 to distribute data between the OLT 110 and the CLT 120. s in the optical portion 150 may include Asynchronous Transfer Mode (APON) PON or broadband PON (BPON) defined by ITU Telecommunication Standardization Sector (ITU-T) document G.983, Gigabit PON (GPON) defined by ITU-T document G.984, and EPON defined by IEEE 802.3ah and 802.3av documents, all of which are incorporated by reference as reproduced in their entirety, PON with wavelength division multiplexing (WDM) (WDM-PON) and Next Generation EPON (NGEPON) is under development by IEEE.

[026] The OLT 110 can be any device configured to communicate with the CNUs 130 through the CLT 120. The OLT 110 can act as an intermediary between the CLTs 120 and/or CNUs 130 and another main network (for example, the Internet). OLT 110 can forward data received from a core network to CLTs 120 and/or CNUs 130 and forward data received from CLTs 120 or CNUs 130 to the core network. Although the specific configuration of the OLT 110 may vary depending on the type of optical protocol deployed in the optical portion 150, in one embodiment, the OLT 110 may comprise an optical transmitter and an optical receiver. When the main network employs a network protocol that is different from the protocol used in the optical portion 150, the OLT 110 can comprise a converter that can convert the main network protocol into the protocol of the optical portion 150. The OLT converter can also convert the optical portion protocol 150 into the main network protocol.

[027] The ODN 115 may be a data distribution system that may comprise fiber optic cables, couplers, splitters, distributors and/or other equipment. In one embodiment, the fiber optic cables, couplers, splitters, distributors and/or other equipment can be passive optical components. Specifically, the fiber optic cables, couplers, splitters, distributors and/or other equipment may be components that do not require any power to distribute data signals between the OLT 110 and the CLT 120. It should be noted that the fiber optic cables can be substituted for any optical transmission medium in some embodiments. In some embodiments, ODN 115 may comprise one or more optical amplifiers. ODN 115 may extend from OLT 110 to CLT 120 and any optional ONUs 170 in a branch configuration as shown in Figure 1, but may alternatively be configured as determined by a person of ordinary skill in the art.

[028] The CLT 120 can be any device or component configured to forward data downstream from the OLT 110 to the corresponding CNUs 130 and forward data upstream from the CNUs 130 to the OLT 110. The CLT 120 can convert the upstream and downstream data appropriately to transfer the data between the optical portion 150 and the coaxial portion 152. The data transferred by the ODN 11 5 can be transmitted and/or received in the form of optical signals and the data transferred by the EDN 135 can be transferred and/or received in the form of electrical signals which can have the same or different logical structure compared to the optical signals. As such, the CLT 120 can encapsulate or frame the data in the optical portion 150 and the coaxial portion 152 differently. In one embodiment, the CLT 120 may include a Medium Access Control (MAC) layer and physical (PHY) layers that correspond to the types of signals carried over the respective medium. The MAC layer can provide channel access control and addressing services to the PHY layers. As such, the PHY may comprise an optical PHY and a coaxial PHY. In many embodiments, the CLT 120 can be transparent to the CNU 130 and the OLT 110 in that frames sent from the OLT 110 to the CNU 130 can be directly addressed to the CNU 130 (e.g., at the destination address and vice versa). As such, the CLT 120 can intermediate between network portions, namely an optical portion 150 and a coaxial portion 152 in the example of Figure 1.

[029] The ONUs 170 can be any devices that are configured to communicate with the OLT 110 and can disconnect the optical portion 150 of the network. ONUs 170 can present customer service interfaces to end users. In some embodiments, an ONU 170 can combine with a CLT 120 to form an FCU.

[030] The electrical portion 152 of the network 100 may be similar to any known electrical communication system. The electrical portion 152 may not require any active components to distribute data between the CLT 120 and the CNU 130. Instead, the electrical portion 152 may use the passive electrical components in the electrical portion 152 to distribute data between the CLT 120 and the CNUs 130. Alternatively, the electrical portion 152 may use some active components, such as amplifiers. Examples of suitable protocols that may be implemented in the electrical portion 152 include MoCA, G.hn, HPNA, and home audio-visual cable.

[031] The EDN 135 may be a data distribution system that may comprise electrical cables (eg, coaxial cables, twisted wires, etc.), couplers, splitters, distributors and/or other equipment. In one embodiment, the electrical cables, couplers, splitters, distributors and/or other equipment can be passive electrical components. Specifically, the electrical cables, couplers, splitters, distributors and/or other equipment may be components that do not require any power to distribute data signals between the CLT 120 and the CNU 130. It should be noted that the electrical cables can be replaced by any electrical transmission medium in some embodiments. In some embodiments, the EDN 135 may comprise one or more electrical amplifiers. EDN 135 may extend from CLT 120 to CNU 130 in a branching configuration as shown in Figure 1, but may alternatively be configured as determined by a person of ordinary skill in the art.

[032] In one embodiment, the CNUs 130 can be any devices that are configured to communicate with the OLT 110, the CLT 120 and any subscriber devices 140. The CNUs 130 can act as intermediaries between the CLT 120 and the subscriber devices 140. For example, the CNUs 130 can forward data received from the CLT 120 to the subscriber devices 140 and can forward r data received from subscriber devices 140 towards the OLT 110. Although the specific configuration of the CNUs 130 may vary depending on the type of network 100, in one embodiment, the CNUs 130 may comprise an electrical transmitter configured to send electrical signals to the CLT 120 and an electrical receiver configured to receive electrical signals from the CLT 120. Additionally, the CNUs 130 may comprise a converter that can convert electrical signals from the CLT 120 into electrical signals for the subscriber devices 140, such as wireless local area network (WiFi) IEEE 802.11 protocol signals. The CNUs 130 may further comprise a second transmitter and/or receiver that can send and/or receive the converted electrical signals to the subscriber devices 140. In some embodiments, the CNUs 130 and coaxial network terminals (CNTs) are similar and therefore are used interchangeably herein. CNUs 130 can typically be located in distributed locations, such as customer premises, but can be located in other locations as well.

[033] The subscriber devices 140 can be any devices configured to interface with a user or a user device. For example, subscriber devices 140 may include desktop computers, laptop-type computers, tablet-type computers, mobile phones, home gateways, televisions, set-top boxes and similar devices.

[034] Figure 2 is a schematic diagram of one embodiment of a DOCSIS 200 network, which may be structurally similar to network 100. The DOCSIS 200 network may be a DOCSIS 3.1 network as specified in the DOCSIS 3.1 document, which is incorporated herein by way of reference as if reproduced in its entirety. The network 200 may comprise a CMTS 210, at least one HFC node 230, any number of CMs 250 and/or digital converter (STB) 252 arranged as shown in Figure 2. Specifically, the HFC node 230 may be coupled to the CMTS 210 via an optical fiber 214 and the CMs 250 and/or STB 252 may be coupled to the HFC node 230 via electrical cables, one or more amplifiers (e.g., amplifiers 236 and 238), and at least one splitter 240. In deployment, the CMTS 210 can be substantially similar to the OLT 110, the HFC node 230 can be substantially similar to a CLT 130, and a CM 250 or a STB 252 can be substantially similar to a CNU 150. It should be noted that the HFC node 230 can be remotely coupled to the CMTS 210 or reside in the CMTS 210. In some embodiments, the CMTS 210 may be equipped with part or all of the functionality of the HFC node 230.

[035] It should be noted that the present disclosure may describe an upstream pilot scheme in the context of an EPoC network (eg, network 100) or a DOCSIS network (eg, network 200). However, a person of ordinary skill in the art will recognize that the upstream pilot scheme described herein can be applied to any network comprising a coaxial segment that employs OFDM P2MP transmission.

[036] Figure 3 is a schematic diagram of an embodiment of an NE 300, which can act as a CLT (for example, CLT 120) or a CMTS (for example, CMTS 210) by implementing any of the schemes described in this document. In some embodiments, the NE 300 can also act as another node(s) in the network, such as a media converter unit that can be coupled to an optical access network and an electrical network with (e.g., coaxial, any Digital Subscriber Line (xDSL), power line, etc.) that employs OFDM transmission. A person skilled in the art will recognize that the term NE encompasses a wide variety of devices of which the NE 300 is merely one example. NE 300 is included for purposes of clarity of discussion, but is in no way intended to limit the application of the present disclosure to a particular NE embodiment or class of NE embodiments. At least some of the features/methods described in the disclosure can be implemented in an appliance or network component such as an NE 300. For example, the features/methods in the disclosure can be implemented using hardware, firmware and/or software installed to run on hardware. As shown in Figure 3, the NE 300 may comprise (Tx/Rx) transceivers 310, which may be transmitters, receivers or combinations thereof. A Tx/Rx 310 may be coupled to the plurality of downstream ports 320 to transmit and/or receive frames from other nodes and a Tx/Rx 310 may be coupled to the plurality of upstream ports 350 to transmit and/or receive frames from other nodes, respectively. A processor 330 may be coupled to Tx/Rx 310 to process the frames and/or determine which nodes to send the frames to. Processor 330 may comprise one or more multi-core processors and/or memory devices 332 which may function as data stores, temporary stores, etc. Processor 330 may be deployed as a general processor or may be part of one or more application specific integrated circuits (ASICs) and/or digital signal processors (DSPs). Processor 330 may comprise an upstream OFDM training module 331, which may deploy an upstream training method, such as method 700 or 800, into a CLT, a CMTS, or any other network nodes that perform upstream training for OFDM transmission, such as a CNU or CM. In an alternative embodiment, the upstream OFDM training module 331 may be implemented as instructions stored in memory devices 332, which may be executed by processor 330. Memory device 332 may comprise a cache for temporary storage content, for example, Random Access Memory (RAM). Additionally, memory device 332 may comprise long-term storage for storing content relatively longer, for example, Read Only Memory (ROM). For example, cache and long-term storage can include dynamic random access memories (DRAMs), solid state drives (SSDs), hard disks, or combinations thereof.

[037] It is understood that by programming and/or loading the executable instructions into the NE 300, at least one of the processors 330 and/or the memory device 332 is(are) changed, which transforms the NE 300 into part of a particular machine or apparatus, for example, a multicore transfer architecture that has the new functionality taught by the present disclosure. It is fundamental to electrical engineering and software engineering that functionality that can be implemented by loading executable software onto a computer can be converted to a hardware implementation by converted design rules. Decisions between deploying a concept in software versus hardware typically depend on considerations of design stability and numbers of units to be produced rather than any issues involved in translating from the software domain to the hardware domain. Generally, it may be preferable for a design that still undergoes frequent change to be deployed in software, as re-trusting a hardware deployment is more expensive than re-trusting a software design. Generally, a design that is stable that will be produced in high volume may be preferable to be deployed in hardware, for example on an ASIC, as for large production hardware deployment can be less expensive than software deployment. Often, a design can be developed and tested in a software form and then transformed, per known design rules, to an equivalent hardware implementation in an ASIC that connects the software instructions. Just as a machine controlled by a new ASIC is a private machine or device, so too a computer that has been programmed and/or loaded with executable instructions can be seen as a private machine or device.

[038] In one embodiment, OFDM transmission may be employed in a coaxial network or a hybrid access network (eg, 100 and/or 200 network) comprising a coaxial segment. In OFDM transmission, digital data can be encoded onto multiple orthogonal subcarrier signals and transmitted in terms of OFDM symbols. An OFDM symbol can be defined as a group of equally spaced frequency subcarriers across an RF spectrum for communications at a predetermined time interval (e.g., a symbol time duration). An OFDM frame can be defined as a group of predefined number of OFDM symbols spanning both time and frequency. A core network access unit (e.g. OFDM P2MP communication system, CLT 120, CMTS 210) may allocate an OFDM frame as a polling frame for upstream channel measurements (e.g. polling). The OFDM symbols within a probe frame may be called probe symbols, and the subcarriers within a probe symbol may be called pilot subcarriers or pilots.

[039] The central access network unit may divide a probe symbol into a plurality of upstream training blocks. For example, each upstream training block may comprise a different subset of pilot subcarriers (e.g., assigned pilot subcarriers) spread across an entire channel bandwidth of the probe symbol with skipped subcarriers (e.g., unassigned pilot subcarriers) between successive assigned pilot subcarriers. As such, the pilot subcarriers in an upstream training block may be non-consecutive (e.g., skipping some pilot subcarriers) in frequency, but may span across the entire upstream spectrum. The central access network unit may assign one or more upstream training blocks in a single probe token to one or more connected downstream network units (eg CNUs 130, CMs 250).

[040] Each downstream network unit may transmit the predetermined sequence according to the assigned upstream training block to enable upstream channel training, where the predetermined sequence may be called a pilot sequence, a polling sequence, or a wideband pilot sequence. For example, each downstream network unit can modulate a pilot sequence according to a Binary Phase Keying (BPSK) modulation scheme and a series of BPSK symbols, map a BPSK symbol to a pilot subcarrier in the probe symbol, and set unassigned pilot subcarriers to zero (e.g., frequency nulls). As such, each downstream network unit may transmit a different portion of the pilot sequence on a different subset of the pilot subcarriers (e.g., assigned pilot subcarriers) and transmit frequency nulls on the unassigned pilot subcarriers, where the unassigned pilot subcarriers may be assigned to the other downstream network unit. Therefore, simultaneous transmissions of the polling symbol from one downstream network unit may not interfere with another downstream network unit.

[041] When the central access network unit receives the polling token, the central access network unit may compute an upstream channel response for each of the downstream network units that transmitted one or more of the upstream training blocks assigned in the polling token. For example, the central access network unit may compute an upstream channel estimate for a downstream network unit by comparing the received signal to the predetermined pilot sequence on the assigned pilot subcarriers of the one or more upstream training blocks that correspond to the downstream network unit and interpolating the computed channel estimates to obtain channel estimates on the frequency subcarriers that are excluded from the one or more assigned upstream training blocks.

[042] In an upstream training embodiment, a central access network unit may determine upstream pre-equalizer taps (e.g., coefficients) according to an estimated upstream channel response to a downstream network unit, and may transmit the pre-equalizer coefficient to the downstream network unit. The downstream network unit may apply an upstream pre-equalizer with the received coefficients before transmitting a signal to the central access network unit. As such, the central access network unit can receive a signal with a fixed response (e.g. with pre-compensated channel distortion) from the downstream network unit and therefore can simplify the upstream channel equalization.

[043] In another upstream training modality, a central access network unit can measure SNR for each subcarrier (e.g., per SNR tone) and determine an appropriate bit loading (e.g., number of data bits) for each subcarrier according to the measured SNR. For example, the central access network unit may assign a higher order modulation scheme (for example, 64 Quadrature Amplitude Modulation (QAM) with six bits per tone, 256 QAM with eight bits per tone) for a high SNR subcarrier and a lower order modulation scheme (for example, BPSK with one bit per tone) for a low SNR subcarrier. Additionally, the central access network unit can dynamically adjust the bit load for each subcarrier to adapt to changes in upstream channel conditions (eg, changing SNRs).

[044] Figure 4 is a schematic diagram of one embodiment of a probe symbol 400 comprising an upstream training block 410 that expands the entire probe symbol 400. The probe symbol 400 may comprise a plurality of pilot subcarriers 411. For example, the probe symbol 400 may comprise 4096 pilot subcarriers for a 4K Fast Fourier Transform (FFT), 2 .048 pilot subcarriers for a 2K FFT, etc. Upstream training block 410 can be assigned with all 4096 pilot subcarriers 411 (eg, active subcarriers) without skipping subcarriers. As such, upstream training block 410 may be employed to transmit a wideband pilot sequence on pilot subcarriers 411 (e.g., from subcarrier zero to 4095 for FFT 4K) on probe symbol 400.

[045] Figure 5 is a schematic diagram of another embodiment of a probe symbol 500 comprising an upstream training block 510. The probe symbol 500 may comprise a plurality of pilot subcarriers 511 and 521. For example, probe symbol 500 may comprise 4096 pilot subcarriers for a 4K FFT, 2048 pilot subcarriers for an FFT 2K, etc. Upstream training block 510 may be assigned with alternate pilot subcarriers 511 and unassigned with pilot subcarriers 521 by skipping a subcarrier 521 between successive assigned pilot subcarriers 511. Skipped subcarriers 521 may be skipped for various reasons, for example, another system may be transmitting on deleted subcarriers 521. As such, the upstream training block 510 may be employed to transmit a portion of a wideband pilot sequence on alternate pilot subcarriers 511 (e.g., assigned pilot subcarriers) in polling symbol 500.

[046] Figure 6 is a schematic diagram of another embodiment of a probe symbol 600 comprising two upstream training blocks 610 and 620. The probe symbol 600 may comprise a plurality of pilot subcarriers 611 and 621. For example, the probe symbol 600 may comprise 4096 pilot subcarriers for a 4K FFT, 2048 pilot subcarriers for a 2K FFT, etc. Upstream training block 610 may start with the lowest frequency subcarrier (e.g. subcarrier zero) and comprise every second pilot subcarrier 611 at probe symbol 600. 0 or 620 may be employed to transmit a different portion of a wideband pilot sequence on pilot subcarriers 611 or 621, respectively. As such, upstream training blocks 610 and 620 can interleave frequencies, but cannot overlap frequencies. It should be noted that a central access network unit (e.g. CLT 120, CMTS 210) may assign the upstream training blocks 610 and 620 to two different downstream network units (e.g. CNUs 130, CMs 250), e.g. the central access network unit may assign the upstream training block 610 to a downstream network unit A and the upstream training block 620 to a downstream network unit B. Therefore, a central access network unit may assign M upstream training blocks to M downstream network units, where each upstream training block may comprise a set of different pilot subcarriers, and successive pilot subcarriers in an upstream training block may be separated by M-1 subcarriers.

[047] In one embodiment of an EPoC network, such as network 100, a CLT (e.g. CLT 120) may allocate a specific polling symbol to a CNU within a polling frame and instruct the CNU (e.g. CNU 130) to transmit a polling sequence in the symbol. The CLT may assign to the CNU all pilots or a subset of pilots (eg scattered) from the assigned sounding symbol. The CNU can transmit pilots that traverse all active subcarriers during the upstream broadband probe. CNU can transmit one pilot per subcarrier. Each pilot can be a predefined BPSK symbol. The OFDM symbol that is used for polling can be defined as a polling symbol. The CLT may employ the upstream SNR measurements and/or the upstream channel estimation in the received polling symbol. For example, the CLT can compute coefficients from an upstream pre-equalizer for each CNU and send the coefficients back to the corresponding CNU. Additionally, the CLT can measure SNR per subcarrier and compute an upstream bit loading table for each CNU. It should be noted that a CNU may not transmit a probe sequence on an excluded subcarrier. Excluded subcarriers may be those subcarriers on which no CNU is allowed to transmit since excluded subcarriers may be on frequencies employed by other systems (eg, including guardband subcarriers). The probing pattern can continue uninterrupted in the presence of excluded subcarriers and/or guard bands. However, the CNU may not transmit any pilots on the excluded subcarrier and/or the guard bands.

[048] In one embodiment of a DOCSIS network, such as the 200 network, upstream broadband polling may be employed during admission and steady state for pre-equalization configuration and time shift variation and periodic transmission power. In a DOCSIS network, a CMTS (e.g., CMTS 210) may assign an OFDM frame for upstream polling, where the polling frame may comprise k contiguous polling symbols (e.g., OFDM symbols), where K is the number of symbols in a minislot (e.g., a group of subcarriers in K number of symbols). The polling frame can be aligned to minislot boundaries in a time domain. A probe symbol may comprise pilots that are BPSK subcarriers, generated by a Pseudo-Random Binary Sequence (PRBS) generation scheme, which may be discussed in more detail below. A CMTS may allocate a specific polling symbol within a polling frame to a CM (eg CM 250) and instruct the CM to transmit a polling sequence in the polling symbol. The CMTS may define a polling pattern comprising pilots of all subcarriers of the assigned polling symbol or a set of pilots of the sparse subcarriers of the assigned polling symbol. A CM can generate a wideband pilot sequence according to the PRBS generation scheme to generate 2048 or 4096 subcarriers for a 2K FFT or 4K FFT, respectively. The CM can employ the same BPSK modulation for a specific subcarrier in all probe symbols. The CM may not transmit a probe sequence on an excluded subcarrier. The CM can transmit zero-valued subcarriers on the excluded subcarriers. Excluded subcarriers may be subcarriers on which no CM is allowed to transmit since excluded subcarriers may be on frequencies employed by another system (eg including guardband subcarriers).

[049] In one embodiment, a wideband pilot sequence may be generated by a predetermined PRBS generation scheme. For example, the polynomial definition for the PRBS scheme might be as shown below:

[050] where a seed of 3071 and a period of 212-1 bits can be used. The 212-1 bits period can be enough to create a polling symbol without repeats. The wideband pilot sequence can be mapped to BPSK pilots. For example, a value of zero can be mapped to a BPSK pilot of one and a value of one(1) can be mapped to a BPSK pilot of minus one. As such, the probe symbol pilots are the BPSK symbols. A poll pilot i can be associated with the ith subcarrier of the symbol, where: n = 0, 1, ..., 4095 for a 4K FFT; and n = 0, 1, ..., 2047 for a 2K FFT.

[051] It should be noted that the subcarriers can be numbered in ascending order starting at zero.

[052] In one embodiment, a central access network unit can assign an upstream training block by specifying a symbol number for upstream probing, an initiating pilot subcarrier number (e.g., ranges from zero to seven), and a number of subcarriers for skipping between successive pilot subcarriers in the symbol. The central access network unit may send the upstream training block allocation in a message (eg, an upstream bandwidth allocation map (MAP) message). For example, the symbol number can be specified in terms of a symbol offset number starting from a polling frame, and the polling frame can be specified in terms of an OFDM frame offset number starting from a frame that corresponds to an allocation start time specified in the message.

[053] In one embodiment of an EPoC network, such as the 100 network, a CLT (eg CLT 120) may specify a polling symbol within a polling frame via a Symbol in Frame parameter. The CLT can allocate subcarriers within the probe symbol by sending two parameters to a CNU (eg CNU 130), a subcarrier start parameter and a subcarrier jump parameter. The start subcarrier parameter may refer to a start subcarrier number and may comprise values ranging from about zero to about seven. The subcarrier hopping parameter can refer to the number of subcarriers to be hopped between successive pilots and can comprise values ranging from about zero to about seven. A value of zero for the skipped subcarrier (for example, subcarrier hopping = 0) can refer to no subcarrier hopping (for example, all subcarriers can be used for polling). For example, upstream training block 410 at probe symbol 400 may be specified with a start subcarrier parameter of zero and a jump subcarrier parameter of zero. Similarly, upstream training block 510 at probe symbol 500 may be specified with a start subcarrier parameter of zero and a subcarrier jump parameter of one. A CLT may specify upstream training block 610 with an initialization subcarrier parameter of value zero and a jump parameter of value one(1) when assigning the upstream training block to a downstream network unit A. Similarly, a CLT may specify upstream training block 620 with an initialization subcarrier parameter of value one(1) and a jump parameter of value one(1) when assigning the upstream training block to a downstream network unit b.

[054] In one embodiment of a DOCSIS network, such as the 200 network, a CMTS (e.g., CMTS 210) can specify a probe symbol within a probe frame via a Symbol in Frame parameter and can specify additional parameters such as a subcarrier start parameter and a subcarrier jump parameter. The start subcarrier parameter can refer to an initiating subcarrier number, and the start subcarrier parameter value can range from about zero to about seven. The skipped subcarrier parameter can refer to the number of subcarriers to be skipped between successive pilots, and the subcarrier parameter value can range from about zero to about seven. A skipped subcarrier parameter value of zero (eg skipped subcarrier = 0) can refer to no skipping of subcarriers, eg all subcarriers in a single symbol can belong to a single transmitter. In such an embodiment, a CM can employ the initiation subcarrier and subcarrier hopping parameters to determine which subcarriers can be employed for polling transmission.

[055] Figure 7 is a flowchart of one embodiment of an upstream training method 700. The method 700 may be deployed by a central access network unit (eg, CLT 120, CMTS 210, and/or NE 300) during upstream training. Method 700 may begin with allocating an OFDM symbol for upstream training in step 710. In step 720, method 700 may divide the OFDM symbol into a plurality of upstream training blocks, where each upstream training block may be specified in terms of an initiating subcarrier number (e.g., an assigned first pilot subcarrier) and a number of subcarriers for skipping between successive pilot subcarriers. For example, each upstream training block may comprise a different number of initiation subcarriers, but may comprise the same number of hop subcarriers. As such, the upstream training blocks may comprise a set of different pilot subcarriers that are not consecutive pilot subcarriers and traverse the upstream frequency spectrum.

[056] In step 730, method 700 may assign the upstream training blocks to one or more downstream network units. At step 740, method 700 may generate a message that indicates the upstream training block assignments. For example, each assignment may comprise an identifier that identifies a downstream network unit for assignment, a polling frame number (for example, the OFDM frame offset from an allocation start time), a symbol number in a polling frame (for example, the OFDM symbol offset from a start of an OFDM frame), an initiation subcarrier number (for example, the subcarrier offset of a lower OFDM symbol frequency) and a subcarrier number jump s between successive pilot subcarriers. It should be noted that in some embodiments, method 700 may generate more than one message to indicate upstream training block assignments depending on the message protocol employed.

[057] In step 750, method 700 may send the message to the downstream network unit. After sending the message to one or more downstream network units, method 700 may wait for the assigned probe symbol to be received from the downstream network unit in step 760. Upon receipt of the probe symbol, method 700 may perform upstream channel estimation and SNR measurements in step 770. For example, method 700 may compute an upstream channel estimate for each downstream network unit on the pilot subcarriers. an upstream training block assigned to the downstream network unit by comparing the received signal value to a predetermined sequence (eg specified by a standard body or a network configuration). After computing the channel estimates on the pilot subcarriers of the upstream training block assigned to the downstream network unit, method 700 may interpolate the computed channel estimates to obtain channel estimates for the skipped subcarriers. It should be noted that method 700 can be applied dynamically or periodically for upstream channel measurement so that upstream transmissions can be adapted for channel variations.

[058] In one embodiment of an EPoC network, such as network 100, a CLT (for example, CLT 120) can schedule a single CNU (for example, CNU 130) in a probe symbol without skipping subcarriers (for example, the upstream training block 410 in the probe symbol 400). In such an embodiment, the CLT can allocate a specific probe symbol to a single CNU and can set a subcarrier jump parameter value to zero and an initiating subcarrier parameter value to a number of the first subcarrier in the probe symbol.

[059] In an alternative embodiment of an EPoC network, such as network 100, a CLT (e.g., CLT 120) may schedule a single CNU (e.g., CNU 130) in a polling symbol with jump subcarriers to create nulls (e.g., upstream training block 510 in polling symbol 500). In such an embodiment, the CLT can allocate a specific probe symbol to a single CNU and can set a subcarrier jump parameter value to the non-zero positive integer value and a start subcarrier parameter value to a number of the first subcarrier in the probe symbol.

[060] In yet another alternative embodiment of an EPoC network, such as network 100, a CLT (e.g., CLT 120) may schedule multiple CNUs (e.g., CNUs 130) in one polling token (eg, polling token 600). In such an embodiment, the CLT may allocate the same probe symbol at any given time to more than one CNU. The CLT can assign a different start subcarrier for each CNU and the same subcarrier hop value for each CNU within the probe symbol. It should be noted that in such an embodiment, the CLT may or may not assign jump subcarriers to create nulls, for example, the CLT may create nulls by specifying a subcarrier jump value equal to or greater than the number of CNUs in the pattern.

[061] Figure 8 is a flowchart of another embodiment of an upstream training method 800. The method 800 may be deployed by a downstream network unit (e.g., the CNU 130, the CM 250, and/or the NE 300) during upstream training. Method 800 may begin with receiving an upstream training block assignment for a specific probe symbol in step 810. For example, the upstream training block assignment may indicate a symbol number (e.g., the offset of a start of an OFDM frame) for the probe symbol, an initiation subcarrier number (e.g., an assigned first pilot subcarrier), and a number of jump subcarriers between successive assigned pilot subcarriers in the probe symbol. gem. In step 820, method 800 may generate a predetermined sequence according to a predetermined generation scheme (e.g., a PRBS scheme). In step 830, method 800 may generate the probe symbol in a frequency domain by modulating the generated sequence on the probe symbol's assigned subcarriers. In step 840, method 800 may set the skipped subcarriers to values of zeros. In step 850, method 800 may perform an Inverse Fast Fourier Transform (IFFT) to transform the probe symbol to a time domain. In step 860, method 800 may transmit the polling token at a time specified by the assignment.

[062] Figure 9 is a schematic diagram of an embodiment of an upstream training message encoding 900. The upstream training message structure 900 may be transmitted by a central access network unit (e.g. CLT 120, CMTS 210) to one or more downstream network units (e.g. CNUs 130, CMs 250) in a hybrid access network (e.g. network 10 0, 200) to indicate the use of symbols in a probe frame. For example, the upstream training message structure 900 can be embedded in a MAP message. Message structure 900 may comprise a plurality of successive probe information elements (P-IEs) 910 that describe the specific usage of symbols within a probe frame (e.g., one P-IE 910 per probe symbol). Each P-IE 910 can be about thirty-two bits in length and the bits within the P-IE 910 can be numbered from bit position zero to bit position thirty-one. Each P-IE 910 may comprise a service flow identifier (SID) field 911, a reserved (R) field 912, a power (PW) field 913, an equalizer (EQ) field 914, an alternating (St) field 915, a polling frame (PrFr) field 916, a Symbol In Frame field 917, a subcarrier field (Start Subp) 91 8 and a subcarrier hop (Subp Hop) field 919. It should be noted that the central access network unit may indicate the successive P-IE 910 in the message frame 900 in a time order (e.g., oldest symbol first) and a subcarrier order (e.g., lowest subcarrier first). Additionally, a polling frame may comprise a combination of allocation polling symbols and non-allocation polling symbols.

[063] The SID 911 field can be about fourteen bits in length and can extend from bit position zero to bit position thirteen. SID field 911 may comprise data indicating a SID that varies for a downstream network unit assigned for use by P-IE 910. R field 912 may be about two bits in length and may extend from bit position fourteen to bit position fifteen. Field R 912 can be reserved for future extension.

[064] PW field 913 may be about one bit in length and may be positioned at bit position fifteen. PW field 913 can indicate whether power control can be employed for polling. For example, PW field 913 may be set to a value of zero to instruct a downstream network unit identified by the SID specified in SID field 911 to transmit with normal power settings and set to a value of one(1) to instruct the downstream network unit to transmit with modified power setting communicated in a Pre-Variation Response (RNG-RSP) message.

[065] EQ field 914 can be about one bit in length and can be positioned at a sixteen bit position. EQ field 914 can indicate whether a transmit equalizer can be employed for polling. For example, EQ field 914 can be set to a value of zero to instruct a downstream network unit identified by the SID specified in SID field 911 to enable the transmit equalizer and set to a value of one(1) to instruct the downstream network unit to disable the transmit equalizer.

[066] The St 915 field can be about one bit in length and can be positioned at a seventeenth bit position. Field St 915 can indicate whether an alternating pattern can be employed for pilot subcarriers. For example, the St field 915 can be set to a value of one(1) to instruct a downstream network unit identified by the SID specified in the SID field 911 to repeat a pattern in the P-IE 910 for the next number of symbols equal in amount to the Subp Jump field 919 and to move the pattern up by one subcarrier on each symbol and pack the pattern back to the beginning. Alternatively, field St 915 can be set to a value of zero to instruct the downstream network unit to employ pilot subcarriers without an alternating pattern.

[067] The PrFr field 916 can be about two bits in length and can extend from bit position eighteen to bit position nineteen. PrFr field 916 may comprise data indicating an offset number of frames from a starting frame at a specified allocation start time in a MAP message carrying message structure 900 and may indicate the first frame to which P-IE 910 is applicable. For example, the PrFr field 916 may be set to a value of zero to indicate a first MAP polling frame.

[068] The Symbol in Frame field 917 can be about six bits in length and can extend from bit position twenty to bit position twenty-five. Symbol in Frame field 917 may comprise data indicating a number of symbol offsets from the start of a polling frame specified in PrFr field 915. For example, Symbol in Frame field 917 may comprise a value ranging from zero to thirty-five, and a value of zero may indicate a first symbol of the polling frame.

[069] The start Subp field 918 can be about three bits in length and can extend from bit position twenty-six through bit position twenty-eight. Initiation Subp field 918 may comprise data indicating an initiation subcarrier to be employed per poll. For example, the Start Subp field 918 can be set to a value of zero to indicate a first subcarrier in a symbol specified by the Symbol In Frame field 917.

[070] The Subp Jump field 919 can be about three bits in length and can extend from bit position twenty-nine to bit position thirty-one. The Subp Hop field 919 may comprise data indicating a number of subcarriers to be skipped between successive pilots in a probe. For example, the Subp Hopping field 919 can be set to a value of zero to indicate no skipping of subcarriers and that all non-deleted subcarriers can be used for polling. It should be noted that the Jump field of subp 919 may indicate additional information when scaling is employed. For example, the value of the Subp Jump field 919 plus one(1) can indicate a total number of symbols to which alternate P-IE allocation can be applied in the polling frame.

[071] Figure 10 illustrates a graph 1000 of an upstream SNR loss embodiment as a function of the number of polling downstream network units in a single polling symbol. The x-axis can represent a number of probe downstream network units per probe symbol, and the y-axis can represent SNR loss in units of decibels (dBs) compared to polling a single downstream network unit. In graph 1000, curves 1010, 1020, 1030, 1040, and 1050 can represent upstream SNR loss versus number of downstream network units probed in a single probe symbol by an Additive White Gaussian Noise (AWGN) channel of 35 dB, 30 dB, 25 dB, 20 dB, and 15 dB, respectively. As can be seen from curves 1010, 1020, 1030, 1040 and 1050, the SNR loss of polling upwards by about four downstream network units in a single symbol can be minimal and the SNR can be comparable to polling one downstream network unit per polling symbol. However, the SNR can gradually degrade as the number of downstream network units increases, and the rate of degradation can vary depending on channel conditions. For example, SNR may degrade at a slower rate (e.g., 1050 curve offset, about 0.1 dB SNR loss for ten polling downstream network units) for a low SNR channel, as channel noise may be dominated by AWGN. Conversely, SNR can degrade at a rapid rate (e.g., 1010 curve deviation, about 3.5 dB SNR loss for ten polling downstream network units) for a high SNR channel (e.g., 35 dB AWGN), as channel noise can be dominated by inaccuracies of upstream channel estimates when multiple downstream network units are polled on a single polling symbol.

[072] At least one embodiment is disclosed and variations, combinations and/or modifications of the embodiment(s) and/or features of the embodiment(s) made by a person of ordinary skill in the art are within the scope of the disclosure. Alternative modalities that result from the combination, integration and/or omission of features of the modality(s) are also within the scope of the disclosure. Where numerical variations or limitations are expressly stated, such express variations or limitations shall be understood to include iterative variations or limitations of similar magnitude that fall within the expressly stated variations or limitations (e.g., from about 1 to about 10 includes 1, 2, 3, 4, etc.; greater than 0.10 includes 0.11; 0.12; 0.13; etc.). For example, whenever a numerical range with a lower bound, Rl, and an upper bound, Ru, is revealed, any number within the range is specifically revealed. In particular, the following numbers within the range are specifically revealed: R = Rl + k * (Ru - Rl), where k is a variable ranging from 1 percent to 100 percent with a 1 percent increment, that is, k is 1 percent, 2 percent, 3 percent, 4 percent, 7 percent, percent, 71 percent, 72 percent, ..., 97 percent, 96 percent, 97 percent, 98 percent, 99 percent or 100 percent. Furthermore, any numerical range defined by two R numbers as defined above is also specifically disclosed. Unless otherwise stated, the term “about” means +10% of the subsequent number. The use of the term "optionally" in relation to any element of a claim means that the element is required, or alternatively, the element is not required, both of which alternatives are within the scope of the claim. The use of broader terms such as comprises, includes and has should be understood as supporting narrower terms such as consists of, essentially comprises of and substantially endowed with. Thus, the scope of protection is not limited by the set of description set out above, but is defined by the claims that follow, the scope includes all equivalents of the subject matter of the claims. Each and every claim is incorporated as further disclosure in the specification and the claims are embodiments of the present disclosure. Discussion of a reference in the disclosure is not an admission that it is not prior art, especially any reference having a publication date after the priority date of this application. The disclosure of all patents, patent applications and publications cited in the disclosure is incorporated herein by reference to the extent that they provide examples, procedures or other details supplementing the disclosure.

[073] While various embodiments have been provided in the present disclosure, it should be understood that the disclosed systems and methods may be incorporated in many other specific ways without departing from the spirit or scope of the present disclosure. These examples are to be considered illustrative and not restrictive and are not intended to be limited to the details given herein. For example, the various elements or components may be combined or integrated into another system or certain features may be omitted or not implemented.

[074] Additionally, techniques, systems, subsystems and methods described and illustrated in various modalities as distinct or separate may be combined or integrated with other systems, modules, techniques or methods without departing from the scope of the present disclosure. Other items shown or discussed as being coupled or communicating with each other may be indirectly coupled or communicating through some interface component, device or intermediary component whether electrically, mechanically or otherwise. Other examples of changes, substitutions and alterations are checked by a person of ordinary skill and could be done without departing from the spirit and scope disclosed in the present document.

Claims (5)

1. A method implemented by a Cable Modem Termination System, CMTS (210), comprising: allocating, by the CMTS (210), a specific polling symbol within a polling frame for wideband polling; defining a polling pattern in the allocated polling symbol, the polling pattern comprising a pilot set of the sparse subcarriers of the allocated polling symbol; and instructing a Cable Modem, CM (250), to transmit a polling sequence on the allocated polling symbol; FEATURED in that instructing the CM (250) to transmit the polling sequence comprises sending an upstream Bandwidth Allocation Map, MAP, message comprising a plurality of successive polling information elements, P-IEs, (910), wherein each P-IE (910) comprises a service flow identifier field (911), a reserved field (912), a power field (913), an equalizer field (914), an alternate field (915), a polling frame field (916), a Symbol in Frame field (917), a start subcarrier field (918) and a subcarrier hop field (919), wherein a parameter in the service flow identifier field (911) indicates a service flow identifier, SID, that varies for a downstream network unit assigned for P-IE use (910); reserved field (912) is reserved for future extension; a parameter in the power field (913) indicates whether the power control can be used for polling; a parameter in the equalizer field (914) indicates whether a transmit equalizer can be employed for polling; a parameter in the alternating field (915) indicates whether an alternating pattern can be employed for pilot subcarriers; wherein the parameter in the alternate field (915), set to a value of one, instructs a downstream network unit identified by the SID specified in the service flow identifier field (911) to repeat a pattern on the P-IE (910) in the next number of symbols equal in amount to the parameter in the subcarrier hop field (919), and move the pattern up by one subcarrier on each symbol and pack the pattern back to the beginning; a parameter in the polling frame field (916) indicates an offset number of frames from a starting frame at an allocation start time specified in the MAP message; a parameter in the Symbol in Frame field (917) specifies the probe symbol within the probe frame, wherein the parameter in the Symbol in Frame field (917) is a symbol offset number from the start of the probe frame; a parameter in the start subcarrier field (918) indicates an start subcarrier to be employed by the probe pattern; and a parameter in the subcarrier hopping field (919) is a number of subcarriers to be skipped between successive pilots in the probing pattern, wherein the parameter in the subcarrier hopping field (919), when set to a value of zero, indicates no subcarrier hopping and that all non-deleted subcarriers may be employed for probing. 2. Method according to claim 1, characterized by the fact that it further comprises instructing the CM (250) to transmit zero-valued subcarriers on exclusion subcarriers in which no CM (250) is allowed to transmit. 3. Method, according to claim 1, CHARACTERIZED by the fact that the probe symbol comprises a Fast Fourier Transform, FFT, of 2,048 points, 2K, or an FFT of 4,096 points, 4k, where the parameter in the start subcarrier field (918) ranges from zero to seven, and in which the parameter in the subcarrier jump field (919) ranges from zero to seven. 4. Method, according to claim 1, CHARACTERIZED by the fact that the probe frame comprises contiguous probe symbols k which are Orthogonal Frequency Division Multiplexing, OFDM symbols, where K is a number of symbols in a minislot and where the probe frame is aligned with minislot boundaries in a time domain. 5. The method of claim 1, characterized in that the alternating field (915) is set to a value of zero to instruct the downstream network unit to employ pilot subcarriers without an alternating pattern.